FIG. 4 schematically shows a structure of a conventional axial gas laser oscillator apparatus. Hereinafter, the structure of a conventional axial gas laser oscillator apparatus will be described with reference to FIG. 4. Discharge tube 901 is made of dielectric material, such as glass. As shown in FIG. 4, electrodes 902 and 903 are disposed in the periphery of discharge tube 901. Power supply 904 is connected to electrodes 902 and 903. Discharge space 905 is formed between electrode 902 and electrode 903 in discharge tube 901. Total reflection mirror 906 and partial reflection mirror 907, which are fixed at each end of discharge space 905, form an optical resonator. Laser beam 908 passes through partial reflection mirror 907 of the optical resonator. Black arrows in FIG. 4 represent the flowing direction of laser gas stream 909 as an amplified medium of the optical resonator. Laser gas stream 909 circulates around laser-gas flow passage 910 of the axial gas laser oscillator apparatus. Bellows section 913 circulates laser gas stream 909, by which laser gas stream 909 flows in discharge space 905 at a current speed of approx. 100 m/sec. Heat exchangers 911 and 912 cool down laser gas stream 909 heated by discharge in discharge space 905 and by the operation of bellows section 913. Laser-gas flow passage 910 communicates with discharge tube 901 at laser-gas leading section 914.
FIG. 5 is a perspective view showing a schematic structure of a conventional gas laser machining apparatus used for sheet-metal cutting. Hereinafter, the conventional gas laser machining apparatus will be described with reference to FIG. 5.
As shown in FIG. 5, laser beam 908 emitted from gas laser oscillator apparatus 900 is reflected off reflection mirror 915 and is guided close to work 916. Laser beam 908 is collected into a high-density energy beam by collecting lens 918 disposed inside torch 917. Irradiated with the energy beam, work 916 fixed on process table 919 undergoes cutting.
Torch 917 moves parallel to plane 919a of process table 919. The relative movement of torch 917 allows work 916 to be processed into a predetermined shape. Torch 917 is driven by X-axis motor 920 or Y-axis motor 921. The conventional gas laser oscillator apparatus and a gas laser machining apparatus are thus structured.
Next, the workings of the apparatus will be described. As shown in FIG. 4, laser gas stream 909 fed from bellows section 913 runs laser-gas flow passage 910 and enters through laser-gas leading section 914 into discharge tube 901. Electrodes 902 and 903 connected to power supply 904 generate a discharge in discharge space 905. Having the discharge energy, laser gas stream 909 in discharge space 905 is pumped. The optical resonator, which is formed of total reflection mirror 906 and partial reflection mirror 907, allows pumped laser gas stream 909 to be in a resonant condition, so that partial reflection mirror 907 outputs laser beam 908. As shown in FIG. 5, laser beam 908 is used for laser-beam machining.
FIG. 6 shows a structure of the bellows section of a conventional gas laser oscillator apparatus. Motor rotor 922 is connected with rotating shaft 923. Impeller 924 is disposed at a tip of rotating shaft 923. Motor stator 926 is secured to supporting member 925 so as to be disposed concentric with motor rotor 922. Receiving AC power from outside, motor stator 926 generates a rotating magnetic field, by which motor rotor 922 rotates. The rotation of motor rotor 922 rotates rotating shaft 923 and impeller 924. In this way, rotating impeller 924 provides laser gas stream 909. Bearings 928 are fixed to rotating shaft 923 at upper and lower sections thereof. Rotating shaft 923 is rotatably retained by bearings 928. Bellows section 913 has a rotating section and a non-rotating section. The rotating section is formed of motor rotor 922, rotating shaft 923, impeller 924, and bearings 928.
The periphery of each of bearings 928 is connected to supporting member 925 as a component of the non-rotating section. Grease 929 is applied to bearings 928 for lubrication.
To lubricate the bearings, for example, Patent Literature 1 introduces a structure in which a grease applying/collecting means is disposed close to the bearings. The conventional gas laser oscillator apparatus, however, has the following problem.
In gas laser oscillator apparatus 900, bellows section 913 is one of the components needing periodic replacement; in particular, bearing 928 is the shortest service life and the lifetime thereof greatly depends on the amount of grease 929. Generally, grease 929 is a volatile substance. Therefore, grease 929 decreases with time since the rotation start of the rotating shaft having impeller 924. Decrease in grease 929 degrades the lubricating performance of grease 929, accelerating wear of bearing 928 and resulting in the short-lived bearing.
Preferably, bellows section 913 should be periodically replaced with a new one, for example, at each periodical inspection. However, if the inspection result tells that bearing 928 seems to be still usable, some users may keep using it without replacement from a cost standpoint. In the worst case, bearing 928 has a sudden breakage without waiting for the next inspection, and accordingly, the whole structure of bellows section 913 has to be halted for a long period.